A quarter-wave plate that converts linearly polarized light into circularly polarized light, a half-wave plate that changes (converts) the plane of vibration of linearly polarized light by 90°, and the like are known as a retardation film that is used for a flat panel display (FPD) and the like. These retardation films can achieve accurate conversion of specific monochromatic light so that ¼λ or ½λ retardation occurs. In recent years, various wideband retardation films that can achieve uniform retardation with respect to light over a wide wavelength band (i.e., retardation films having reverse wavelength dispersion) have been studied (see Patent Literature 1 to 6, for example).
It has been desired to reduce the thickness of the flat panel display as much as possible along with an improvement in functionality and widespread use of mobile information terminals (e.g., mobile personal computer and mobile phone). Therefore, a reduction in thickness of the retardation film has also been desired.
It has been considered that the thickness of the retardation film can be effectively reduced by producing the retardation film by applying a polymerizable composition that includes a low-molecular-weight polymerizable compound to a film substrate. Various low-molecular-weight polymerizable compounds having excellent wavelength dispersion, and various polymerizable compositions using such polymerizable compounds have been developed (see Patent Literature 7 to 24, for example).
However, the low-molecular-weight polymerizable compounds or the polymerizable compositions disclosed in Patent Literature 7 to 24 have a number of problems in that the reverse wavelength dispersion may be insufficient, or it may be difficult to apply the low-molecular-weight polymerizable compounds or the polymerizable compositions to a film due to a high melting point that is not suitable for an industrial process, or the temperature range in which the liquid crystallinity is obtained may be very narrow, or the solubility in a solvent commonly used for an industrial process may be low. Moreover, since these low-molecular-weight polymerizable compounds and the like are synthesized through a plurality of steps using a synthesis method that utilizes an expensive reagent, an increase in production cost occurs.
Since an optical defect occurs when ionic impurities (e.g., halogen or alkali) are included in a compound used to produce an optical member, it has been desired to reduce the ionic impurity content when producing a polymerizable compound.